Circuit-forming charging powder and multilayer wiring board using the same

ABSTRACT

A circuit-forming charging powder allowing circuit patterns to resist being peeled off a printing object when the powder is used for printing a circuit pattern by an electrophotographic method on the object, wherein the circuit-forming charging powder has a conductive metal powder, a charge control agent and an adhesion reinforcing agent combined with a heat-melt resin and a method for producing the circuit-forming charging powder, as well as printed objects and multilayer wiring boards are described.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a circuit-forming chargingpowder and a multilayer wiring board using the same, especially to acircuit-forming charging powder (toner) to be used in printing a circuitpattern on an object by electrophotography, and a multilayer wiringboard using the same.

[0003] 2. Description of the Related Art

[0004] Japanese Unexamined Patent Publication No. 4236484 discloses amethod for forming a desired circuit pattern on an insulating substrateby taking advantage of the electrostatic force used in conventionalelectrophotography, and a circuit-forming charging powder to be used inthis wiring method. FIG. 1 shows a cross section of the conventionalcircuit-forming charging powder. The circuit-forming charging powder 100with a mean particle size of 10 to 15 μm assumes a structure in which aconductive metal powder 101 and a charge control agent 102 are uniformlydispersed in a heat-melt resin 103. The practical method for producingthe circuit-forming charging powder 100 comprises the steps of: mixing aflake-shaped silver powder with a mean particle size of 0.4 μm as aconductive metal powder 101, a metallic azo dye as a charge controlagent 102 and a styrene-acrylic acid copolymer as a heat-melt resin 103in a weight ratio of 80:1:19, respectively; and heat-melting the mixturefollowed by kneading with a kneader. Then, the mixture is roughlycrushed with a cutter mill, finely crushed with a jet mill andclassified with an air jet, thereby obtaining the circuit-formingcharging powder 100.

[0005] However, the conventional circuit-forming charging powderinvolves a problem in that the circuit pattern can peel off the bakedceramic sheet when the powder is used for printing the circuit patternon a ceramic green sheet by electrophotography because the ceramic greensheet shrinks during baking.

SUMMARY OF THE INVENTION

[0006] Accordingly, the object of the present invention, carried out forsolving the problem described above, provides a circuit-forming chargingpowder having little possibility for allowing the circuit pattern to bepeeled off the printing object even when the circuit pattern is printedon the printing object by electrophotography, and a multilayer circuitboard using the same.

[0007] According to the present invention, the circuit-forming chargingpowder to be used for printing a circuit pattern on a printing object byelectrophotography comprises a conductive metal powder, a heat-meltresin, a charge control agent and an adhesion reinforcing agent.

[0008] The conductive metal powder is a secondary powder comprisingaggregates formed by aggregating a plurality of primary powders, and theprinting object is a ceramic green sheet.

[0009] The multilayer wiring board according to the present invention isformed by laminating and baking the ceramic green sheets on which thecircuit pattern is printed.

[0010] The circuit-forming charging powder according to the presentinvention contains the adhesion reinforcing agent, which serves forallowing the conductive metal powder used for forming the circuitpattern to adhere with the baked ceramic sheet when the ceramic greensheet on which the circuit pattern has been printed is baked.Accordingly, the adhesion strength between the baked ceramic sheet andthe circuit pattern is improved after baking, preventing the circuitpattern from being peeled off the ceramic sheet.

[0011] Also, the conductive metal powder constituting thecircuit-forming charging powder is a secondary powder comprising anaggregate prepared by aggregating a plurality of primary powders, theconductive metal powder comprising the secondary powder beingdissociated into primary powders when the circuit-forming chargingpowder is fixed. Accordingly, the circuit pattern formed with theprimary powders constituting the conductive metal powder is denselypacked, allowing the sheet resistance of the circuit pattern to befurther reduced along with decreasing the circuit pattern loss.

[0012] Also, the adhesion reinforcing agent contained in thecircuit-forming charging powder serves to allow the conductive metalpowder to be formed into the circuit pattern and adhered with the bakedceramic sheet when the ceramic sheet on which the circuit pattern hasbeen printed. Consequently, the adhesion strength of the baked ceramicsheet with the circuit pattern is improved after baking, prevent thecircuit pattern from being peeled off the ceramic sheet.

[0013] Also, the multilayer wiring board according to the presentinvention is produced by the steps comprising: printing the circuitpattern on the ceramic green sheet by the electrophotographic methodusing the circuit-forming charging powder containing the adhesionreinforcing agent; and laminating the ceramic green sheets followed bybaking. Accordingly, the circuit pattern has essentially no possibilityto be peeled off the baked ceramic sheet after baking, making itpossible to improve quality and reliability of the multilayer wiringboard that can be used in high frequency bands.

[0014] Also, the multilayer wiring board is produced by the stepscomprising: preparing the circuit-forming charging powder containing theconductive metal powder comprising the secondary powder of aggregates ofa plurality of primary powders; and laminating the ceramic green sheet,on which the circuit pattern is printed by the electrophotographicmethod using the circuit-forming charging powder, followed by baking.Therefore, ceramic sheet resistance and loss of the circuit pattern isreduced along while making it possible to use the multilayer wiringboard in higher frequency bands.

[0015] Other features and advantages of the present invention willbecome apparent from the following description of the invention whichrefers to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 shows a cross section of the conventional circuit-formingcharging powder;

[0017]FIG. 2 shows a cross section of the circuit-forming chargingpowder according to the first preferred embodiment of the presentinvention;

[0018]FIG. 3 shows a cross section of the circuit-forming chargingpowder according to the second preferred embodiment of the presentinvention;

[0019]FIG. 4 shows a cross section of the circuit-forming chargingpowder according to the third preferred embodiment of the presentinvention;

[0020]FIG. 5 illustrates the structure of the electro-photographicsystem to be used in forming the circuit pattern on the printing object;

[0021]FIG. 6 shows a cross section of the multilayer wiring boardaccording to the present invention; and

[0022]FIG. 7 shows one example of the cross section of the conductivemetal powder constituting the circuit-forming charging powder shown inFIG. 2 to FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0023]FIG. 2 shows a cross section of the circuit-forming chargingpowder in the first preferred embodiment according to the presentinvention. The circuit-forming charging powder 10 assumes a structure inwhich a conductive metal powder 11, a charge control agent 12 and anadhesion reinforcing agent 13 are uniformly dispersed in a heat-meltresin 14.

[0024] A practical method for producing the circuit-forming chargingpowder 10 will be described. In the first step, spherical copperparticles with a mean particle size of 0.8 μm as the conductive metalpowder 11, a metallic azo dye as a charge control agent 12, silica as anadhesion reinforcing agent 13 and a styrene-acrylic acid copolymer as aheat-melt resin 14 are mixed in a weight ratio of 93:1:1:5,respectively.

[0025] In the next step, the mixture is heat-melted and kneaded in akneader, followed by a rough crushing with a cutter mill and a finecrushing with a jet mill. The circuit-forming charging powder 10 with amean particle size of 8.0 μm is obtained by classification with air jet.

[0026] According to the circuit-forming charging powder in the firstpreferred embodiment, the adhesion reinforcing agent contained thereinserves for reinforcing the adhesion of the printing object with theconductive metal powder to be formed into a circuit pattern, preventingthe circuit pattern from being peeled off the printing object due toenhanced adhesion strength of the printing object with the circuitpattern.

[0027] The content of the adhesion reinforcing agent contained in thecircuit-forming charging powder can be desirably adjusted since it iskneaded with the heat-melt resin, enabling adhesion strength of thebaked ceramic green sheet with the circuit pattern to be adjusted. Alarge quantity of the adhesion reinforcing agent may be even containedin the circuit-forming charging powder in order to obtain higheradhesion strength.

[0028] When the printing object is a ceramic green sheet, the adhesionreinforcing agent contained in the circuit-forming charging powderserves to allow the conductive metal powder forming the circuit patternto adhere to the baked ceramic sheet during baking of the ceramic greensheet on which the circuit pattern has been formed. Therefore, adhesionstrength of the baked ceramic sheet with the circuit pattern is enhancedto prevent the circuit pattern from being peeled off the ceramic sheet.

[0029]FIG. 3 shows a cross section of the circuit-forming chargingpowder according to the second preferred embodiment of the presentinvention. An outer wall 21 comprising the adhesion reinforcing agent 13and heat-melt resin 14 is formed around the conductive metal powder 11in the circuit-forming charging powder 20, assuming a structure in whichthe charge control agent 12 is adhered on the surface of the outer wall21.

[0030] A practical method for producing the circuit-forming chargingpowder 20 will be described hereinafter. In the first step, copperparticles with a mean particle size of 5.0 μm as the conductive metalpowder 11 and particles, obtained by mixing silica as the adhesionreinforcing agent 13 and a styrene-acrylic acid copolymer as theheat-melt resin 14 in a weight ratio of 1:5 followed by finely crushing,are mixed in a weight ratio of 93:6, allowing the particles comprisingthe adhesion reinforcing agent 13 and heat-melt resin 14 to adhere onthe conductive metal powder 11 by electrostatic force.

[0031] In the next step, a mechanical impact force is applied to theproduct obtained by adhering the particles comprising the adhesionreinforcing agent 13 and the heat-melt resin 14 to the conductive metalpowder 11 to form an outer wall 21 comprising the adhesion reinforcingagent 13 and heat-melt resin 14 around the conductive metal powder 11.

[0032] In the third step, the product prepared by forming the outer wallcomprising the adhesion reinforcing agent 13 and heat-melt resin 14around the conductive metal powder 11, and a azo metallic dye as thecharge control agent 12 are mixed in a weight ratio of 99:1, followed byapplying a mechanical impact force to form a circuit-forming chargingpowder 20 with a mean particle size of 8.0 μm in which the chargecontrol agent 12 is adhered on the surface of the outer wall 21. Inother words, the outer wall 21 comprising the adhesion reinforcing agent13 and heat-melt resin 14 is formed around the conductive metal powder11 to obtain the circuit-forming charging powder 20 on the surface ofwhich the charge control agent 12 is adhered.

[0033] In the circuit-forming charging powder according to the secondpreferred embodiment described above, a circuit-forming charging powderthat can be uniformly charged is obtained by adhering the charge controlagent on the surface of the outer wall formed around the conductivemetal powder. Accordingly, use of this circuit-forming charging powderallows the charge to be more easily controlled as well as improving theprinting affinity for complying with circuit patterns having narrowintervals, making it possible to form a circuit pattern with low sheetresistance.

[0034] The conductive metal powder is prevented from being exposed onthe surface of the circuit-forming charging powder because the outerwall comprising the adhesion reinforcing agent and heat-melt resin isformed around the conductive metal powder. Therefore, the chargingability of the circuit-forming charging powder is improved by preventingdeterioration of charging ability ascribed to the conductive metalpowder, consequently improving printing affinity even more to complywith the circuit pattern having narrower intervals.

[0035] The quantity of the adhesion reinforcing agent contained in thecircuit-forming charging powder can be adjusted to a desirable levelsince it is kneaded with the heat-melt resin forming the outer wall,thereby enabling one to adjust the adhesion strength of the bakedceramic sheet with the circuit pattern. In order to reinforce theadhesion strength, a large amount of the adhesion reinforcing agent canbe also included in the circuit-forming charging powder.

[0036]FIG. 4 shows a cross section of the circuit-forming chargingpowder according to the third preferred embodiment of the presentinvention. The circuit-forming charging powder 30 assumes a structurecomprising the charge control agent 12, adhesion strength reinforcingagent 13 and heat-melt resin 14 formed around the conductive metalpowder 11.

[0037] A practical method for producing the circuit-forming chargingpowder 30 will be described hereinafter. In the first step, copperparticles with a mean particle size of 5.0 μm as the conductive metalpowder and particles, prepared by mixing a metallic azo dye as thecharge control agent 12, silica as the adhesion reinforcing agent 13 anda styrene-acrylic acid copolymer as the heat-melt resin 14 in a weightratio of 1:1:5 followed by finely crushing, were mixed in a weight ratioof 93:7, thereby allowing the particles comprising the charge controlagent 12, adhesion reinforcing agent 13 and heat-melt resin 14 to adhereon the conductive metal powder 11.

[0038] In the next step, a mechanical impact force is applied to theconductive metal powder 11 adhered with particles composed of the chargecontrol agent 12, adhesion reinforcing agent 13 and heat-melt resin 14,thus obtaining the circuit-forming charging powder 30 with a meanparticle size of 8.0 μm in which an outer wall comprising the chargecontrol agent 12, adhesion reinforcing agent 13 and heat-melt resin 14is formed around the conductive metal powder 11.

[0039] In the circuit-forming charging powder according to the thirdpreferred embodiment, the surface of the circuit-forming charging powderis not required to be separately adhered with the charge control agentbecause the outer wall comprising the charge control agent, adhesionreinforcing agent and heat-melt resin has been formed around theconductive metal powder, enabling one to simplify the productionprocess, as well as to reduce the production cost, of thecircuit-forming charging powder.

[0040] As shown in the foregoing first to third preferred embodiments,increasing the content of the conductive metal powder in thecircuit-forming charging powder to more than about 90 wt %, e.g., to 93%wt, allows the film thickness of the circuit pattern to be thicker byuse of one printing process. Therefore, the sheet resistance of thecircuit pattern can be reduced as well as diminishing the circuitpattern loss, thus allowing the multilayer printed board obtained byusing this circuit-forming charging powder to be used in high frequencybands.

[0041] Forming a thick circuit pattern in one printing makes it possibleto simplify the production process of the circuit pattern, reducing theproduction cost of the multilayer wiring board. Shift and deformation ofthe printed circuit pattern may be also avoided to further improve thequality of the multilayer wiring board

[0042] In addition, since the content of the heat-melt resin in thecircuit-forming charging powder can be reduced to less than about 10 wt%, e.g., to 5 wt %, frequency of delamination between the circuitpattern and baked ceramic sheet that occurs due to complete combustionof the heat-melt resin during baking can be reduced, enabling one toform a more reliable circuit pattern.

[0043] The content of the conductive metal powder is preferably lessthan about 98% by weight since when the content of the conductive metalpowder is more than about 98% by weight, it becomes difficult toperfectly cover the conductive metal powder with the heat-melt resinwithout exposing the powder surface.

[0044]FIG. 5 illustrates the construction of the electrophotographicsystem to be used in forming the circuit pattern on the printing object.Forming the circuit pattern on the printing object comprises the stepsof: charging the surface of a photosensitive member 41 with a coronacharging device 42; exposing the surface of the photosensitive member 41rotating along the direction indicated by an arrow A by irradiating witha laser beam 43 to form latent images (not shown in the drawing);developing the latent image on the surface of the photosensitive member41 by electrostatic adsorption of the circuit-forming charging powder 10to 30 fed from a feed means 44; transferring the circuit-formingcharging powder 10 to 30 developed on the latent image pattern on theprinting object 45 by rotating the photosensitive member 41; and fixingthe circuit-forming charging powder 10 to 30 transferred on the printingobject 45 by irradiating with a flash lamp 46 to form the circuitpattern (not shown in the drawing) on the printing object 45.

[0045]FIG. 6 shows a cross section of a multilayer wiring boardaccording to one preferred embodiment of the present invention. Themultilayer wiring board 50 is provided with the first, second and thirdgreen sheets represented by 51 a, 51 b and 51 c, respectively. Circuitpatterns 52 a and 52 b are printed on the first green sheet 51 a andsecond green sheet 51 b using the circuit-forming charging powder 10 to30 (FIG. 2 to FIG. 4) in the foregoing first to third preferredembodiments with the electro-photographic system in FIG. 4. Then, theceramic green sheets 51 a to 51 c are laminated under pressure to form amonolithic member followed by baking.

[0046] The circuit patterns 52 a and 52 b on the ceramic green sheets 51a and 51 b are put into electrical continuity with pier holes 53, whichcan be formed using currently available technologies. For example, apier hole is produced by injecting electric conductors for each pierhole using a conductor drawing apparatus. It is preferable in thismethod to form the pier hole 53 prior to forming the circuit patterns 52a and 52 b since the powder may possibly damage the nozzle of thedrawing apparatus when the pier hole 53 is formed after forming thecircuit patterns 52 a and 52 b by the electrophotographic method.

[0047] The multilayer wiring board as described above is produced byprinting the circuit pattern by the electrophotographic method on theceramic green sheet, followed by laminating and baking the green sheets.Consequently, there is essentially no possibility that the circuitpattern is peeled off the baked ceramic sheet, thus improving thequality and reliability of the multilayer wiring board. Accordingly, themultilayer wiring board can be used in high frequency bands.

[0048] Although copper was used for the circuit forming charging powderin the first to third embodiments, the same effect as described in theseembodiments can be obtained by using a metal such as gold, silver,nickel, palladium or molybdenum, or an alloy comprising two or morekinds of these metals. The materials used heretofore can also be used inthis invention.

[0049] Although a styrene-acrylic acid copolymer was used for theheat-melt resin in the foregoing embodiments, the same effect asdescribed in these embodiments can be obtained by using a resin such aspolymethyl methacrylate resin, cross-linked acrylic acid resin,polystyrene resin, polyethylene resin, fluorinated resin, fluorinatedvinylidene resin and benzoguanamine resin, or a mixture of two or moreof these resins. The materials used heretofore can also be used in thisinvention.

[0050] Although a metallic azo dye was used for the charge control agentin the examples, the same effect as described in the foregoingembodiments can be obtained by using a negatively charged charge controlagent such as a chlorinated paraffin, a chlorinated polyester, anacid-excess polyester, a sulfonylamine naphthenic acid metal salt ofcopper phthalocyanine, a metal salt of fatty acid and resinate soap, ora mixture of two or more of these compounds. The materials usedheretofore can also be used in this invention.

[0051] Although silica glass was used for the adhesion reinforcing agentabove, the same effect as described in the foregoing embodiments can beobtained by using a substance such as borolilicate glass, soda lime,lead glass and aluminosilicate glass, or a glass comprising a mixture oftwo or more of these substances, or a ceramic comprising alumina andferrite.

[0052] As shown in FIG. 7, the conductive metal powder 11 constitutingthe circuit-forming charging powders 10 to 30 may be a secondary powdercomprising an aggregate in which a plurality of primary powders 15 areaggregated. Since the conductive metal powder 11 comprising thesecondary powders is dissociated into the primary powders 15 when thecircuit-forming charging powders 10 to 30 are fixed, packing of thecircuit pattern formed by the primary powder 15 constituting theconductive metal powder is made dense, making it possible to furtherreduce the sheet resistance of the circuit pattern along with furtherdecreasing the circuit pattern loss. Consequently, the multilayer wiringboard produced by using this circuit-forming charging powder can be usedin higher frequency bands. It is especially preferable for obtaining aspherical secondary powder that the particle size of the primary powderis within the range of ⅕to {fraction (1/20)}of the particle size of thecircuit-forming charging powder.

[0053] It is preferable that the particle size of the circuit-formingcharging powder is in the range of about 3 to 20 μm for enhancing theeffect of the present invention.

[0054] Although the adhesion reinforcing agent contained in thecircuit-forming charging powder is kneaded with the heat-melt resin andincorporated into the outer wall in the circuit-forming charging powderaccording to the second and third preferred embodiments, the agent maybe adhered on the surface of the circuit-forming charging powder, or onthe surface of the outer wall, without being kneaded with the heat-meltresin.

[0055] The structure in which the charge control agent is adhered on theperiphery of the circuit-forming charging powder, or the structure inwhich charge control agent is adhered on the surface of the outer wallcomprising the charge control agent, adhesion reinforcing agent andheat-melt resin can display the same effect in the circuit-formingcharging powder according to the third preferred embodiment.

[0056] While the invention has been particularly shown and describedwith reference to preferred embodiments thereof, it will be understoodby those skilled in the art that the forgoing and other changes in formand details may be made therein without departing from the spirit of theinvention.

What is claimed is:
 1. A circuit-forming charging powder for use in printing a circuit pattern on an object by electrophotography, comprising a conductive metal powder, a heat-melt resin, a charge control agent and an adhesion reinforcing agent.
 2. The circuit-forming charging powder according to claim 1 , wherein said conductive metal is at least one member selected from the group consisting of copper, gold, silver, nickel, palladium or molybdenum.
 3. The circuit-forming charging powder according to claim 1 , wherein said charge control agent is at least one member selected from the group consisting of a metallic azo dye, a chlorinated paraffin, a chlorinated polyester, an acid-excess polyester, a sulfonylamine naphthenic acid metal salt of copper phthalocyanine, a metal salt of fatty acid and resinate soap.
 4. The circuit-forming charging powder according to claim 1 , wherein said adhesion reinforcing agent is at least one member selected from the group consisting of silica glass, borosilicate glass, soda lime, lead glass, aluminosilicate glass, alumina and ferrite.
 5. The circuit-forming charging powder according to claim 1 , wherein the particle size of said circuit-forming charging powder is in the range of about 3 to 20 μm.
 6. The circuit-forming charging powder according to claim 1 , wherein the content of said conductive metal powder in the circuit-forming charging powder is more than about 90 wt % and less than or equal to about 98 wt %.
 7. The circuit-forming charging powder according to claim 1 , wherein the content of said heat-melt resin in the circuit-forming charging powder is less than about 10 wt %.
 8. The circuit-forming charging powder according to claim 7 , wherein the content of said conductive metal powder in the circuit-forming charging powder is more than about 90 wt % and less than or equal to about 98 wt %. and wherein the particle size of said circuit-forming charging powder is in the range of about 3 to 20 μm.
 9. The circuit-forming charging powder according to claim 8 , wherein said adhesion reinforcing agent is at least one member selected from the group consisting of silica glass, borosilicate glass, soda lime, lead glass, aluminosilicate glass, alumina and ferrite.
 10. The circuit-forming charging powder according to claim 9 , wherein said conductive metal is at least one member selected from the group consisting of copper, gold, silver, nickel, palladium or molybdenum, and wherein said charge control agent is at least one member selected from the group consisting of a metallic azo dye, a chlorinated paraffin, a chlorinated polyester, an acid-excess polyester, a sulfonylamine naphthenic acid metal salt of copper phthalocyanine, a metal salt of fatty acid and resinate soap.
 11. An aggregate of a plurality of circuit-forming charging powder particles according to claim 10 .
 12. An aggregate of a plurality of circuit-forming charging powder particles according to claim 1 .
 13. A ceramic green sheet having a circuit pattern which comprises the circuit-forming charging powder according to claim 12 thereon.
 14. A ceramic green sheet having a circuit pattern which comprises the circuit-forming charging powder according to claim 11 thereon.
 15. A ceramic green sheet having a circuit pattern which comprises the circuit-forming charging powder according to claim 4 thereon.
 16. A ceramic green sheet having a circuit pattern which comprises the circuit-forming charging powder according to claim 1 thereon.
 17. A multilayer wiring board comprising a baked laminate comprising a plurality of ceramic green sheets of claim 16 .
 18. A multilayer wiring board comprising a baked laminate comprising a plurality of ceramic green sheets of claim 15 .
 19. A multilayer wiring board comprising a baked laminate comprising a plurality of ceramic green sheets of claim 14 .
 20. A multilayer wiring board comprising a baked laminate comprising a plurality of ceramic green sheets of claim 13 . 